The research proposed is to investigate the mechanism of transcriptional regulation of mouse histone genes during the cell cycle and during development. This will be done by obtaining more mouse histone gene clones than are currently available with an emphasis on obtaining clones of replacement variant histone genes. The purpose of obtaining more clones is to use them as probes. Another reason for obtaining more clones is to see how the structure and organization of the different types of histone genes are related to their expression. We will use mouse histone genes as probes to determine if the steady state mRNA levels and transcription of the replication variant histone genes and replacement variant histone genes change during differentiation of mouse erythroleukemia (MEL) cells. Also, we will determine if the steady state mRNA levels and transcription of the replacement variant histone genes change in 3T3 cells between a serum starved G-O phase and S phase of the cell cycle. These steady state levels will be determined using an S-1 nuclease assay. The transcriptional rates will be determined using tritiated uridine pulse labeling and in vitro nuclei transcription. We will establish an assay to look for factors which regulate histone gene transcription during the cell cycle in 3T3 mouse fibroblasts and during differntiation of MEL cells. Our primary factor assay system will be an in vitro nuclear transcription system. Alternatively, we will look for transcriptional regulators with permeabilized cells or chromatin dependent transcription. A nitrocellulose filter binding assay will also be used to look for proteins which may specifically affect transcription of histone genes.